For a long time, different kinds of implants produced from various materials have been used in the treatment of patients, for fixation of fractures, as a substitute for removed bone tissue, in dental surgery for fixation of a denture or dental bridge, and in other applications, for example. In the end of the 19th century, experiments with different kinds of implant materials, such as gold, porcelain, and silver were performed. In the 1930s, the use of the metal alloy vitallium was suggested, which is a biocompatible material on which a lot of research has been conducted since then, and which is still used today. The advantageous biocompatibility of titanium was discovered by accident in the 1950s, when a titanium implant was found to be able to integrate with bone tissue. This formed the basis of the concept of osseointegration. Since then, titanium, due to its good biocompatibility, has been used for implants, in pure form or in the form of alloys. With time, titanium and titanium alloys showed superior long term results, inter alia, titanium was found to be non-carcinogenic, which results are well documented. However, in the beginning, the use of titanium and titanium alloys in implants was limited to bone tissue of good quality due to their relative bionert properties, i.e., inability to interact with biological systems, in contrast to more bioactive materials which better can interact with biological systems, such as surrounding tissue.
There are substantially two procedures to modify the surface in order to enhance the ability of the implant to interact with the surrounding tissue. One of these is a topographical modification of the implant, for example by patterning or raising/texturing the surface to improve the contact between the implant and the tissue, and the other one is a chemical modification of the surface of the implant, but also a combination of these two procedures is possible.
Today, for the chemical modification of the surface, there are several known suitable bioactive materials which have the ability to interact with biological systems and which, for example, can be applied to the outer surface of the implant by different deposition techniques, such as plasma-spraying, pulsed-laser deposition, sputtering, blast-coating etc. Examples of such bioactive materials are, for example, calcium phosphates, such as hydroxyapatite and tricalcium phosphate.
However, there are drawbacks associated with the use of new materials and substances, as their long-term effects are unknown.
There is a need to tailor the interaction of an implant with biological tissue. It is previously known to produce implants of two different materials, where the first material covers one part of the surface of the implant and a second material covers the other part of the surface of the implant. Hereby, it is possible, to a certain degree, to adapt an implant to different requirements. However, this solution is not flexible enough and does not provide implants which are adaptable enough.
Further, there is a need to tailor the interaction of an implant with biological tissue such that an implant with a surface having bioactive properties is provided, which thereby interacts with the surrounding tissue, and at the same time has well documented long-term effects.